PROJECT SUMMARY Stroke is the most common fatal neurological disease and a leading cause of serious long-term disability in the United States. Each year, approximately 800,000 people suffer a stroke and more than 140,000 people die from stroke in the U.S. However, there is only one FDA-approved drug for ischemic stroke, the tissue plasminogen activator (tPA), which is beneficial to patients only within a few hours of having a stroke. Hence there is an urgent need to identify novel therapeutic targets for treatment of this devastating disease. The rapid decrease of oxygen and glucose in brain tissue after the ischemic stroke can trigger necrotic neuronal cell death within minutes. The main underlying cause is the dysregulation of major intracellular ion concentrations (sodium, potassium and chloride), but it remains unclear which particular ion channels are activated by ischemic conditions and thus play an important role in the pathological ion fluxes. Accumulating evidence suggest that chloride influx is one of the key mechanisms leading to ischemia-evoked neuronal edema and tissue injury. We recently performed an unbiased RNAi screen and identified a novel chloride channel, which has been implicated in ischemic cytotoxicity through mediating chloride influx and cell swelling. The proposed research project will combine molecular biology, electrophysiology, mouse genetics, and various in vitro and in vivo experimental stroke models to elucidate the gating mechanisms of this novel chloride channel and determine its pathological role in ischemic cytotoxicity and stroke. Completion of the proposed study on this novel chloride channel family will shed light on its regulatory mechanisms and pathological function, which may lead to new therapeutic strategies for ischemic stroke and other neurodegenerative diseases.